The present invention relates to novel heterocyclic compounds, and more particularly to materials for light emitting devices that can convert electric energy to light to emit the light. The invention further relates to light emitting devices which can be suitably used in the fields of display elements, displays, back lights, electrophotography, illuminating light sources, recording light sources, reading light sources, indicators, signboards and interior decorations.
At present, the research and development of various display elements have been actively made. In particular, organic electroluminescence (EL) devices have attracted attention as promising display devices, because luminescence of high luminance can be obtained at low voltage. For example, a light emitting device in which an organic thin film is formed by vapor deposition of an organic compound (Applied Physics Letters, 51, 913 (1987)) has been known. The light emitting device described in this literature is substantially improved in light emitting characteristics compared with conventional monolayer elements, by using tris(8-hydroxyquinolinato)aluminum complex (Alq) as an electron transporting material and laminating a hole transporting material (amine compound) therewith.
As means for further improving the light emitting efficiency of the laminated light emitting devices, methods of doping the elements with fluorescent dyes have been known. For example, elements doped with coumarin dyes, described in Journal of Applied Physics, 65, 3610 (1989), are substantially improved in light emitting efficiency compared with elements not doped therewith. In this case, it is possible to take out light having a desired wavelength by changing the kind of fluorescent compound. However, when Alq is used as the electron transporting material, an increase in driving voltage for obtaining high luminance results in observation of green luminescence of Alq in addition to luminescence of the fluorescent compound used for doping. Accordingly, blue luminescence suffers from the problem of a reduction in color purity, so that the development of host materials which do not reduce the color purity has been desired. For improving this disadvantage, specified indole derivatives are disclosed in JP-A-10-92578 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) and U.S. Pat. No. 5,766,779. However, the compounds described therein have the problem that an increase in driving voltage is required for luminescence of high luminance. Accordingly, the development of compounds in which luminescence of high luminance is possible at low voltage has been desired.
As methods for increasing the light emitting efficiency, methods are reported in which hole blocking materials such as 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (TAZ) and bathocuproin (BCP) are used. However, the use of these known materials has raised a serious problem with regard to durability, particularly deterioration of the elements with time in storing at high temperatures in continuous luminescence.
The conventional elements good in color purity and high in light emitting efficiency are ones in which charge transporting materials are doped with fluorescent dyes in slight amounts, and have the problems that it is difficult to give the reproducibility of element characteristics from the production point of view, and that the long-term use thereof causes a reduction in luminance and changes in color because of low durability of the dyes. As means for solving the problems, the development of materials having both the charge transporting function and the luminescent function has been desired. However, the materials that have hitherto been developed have the problem that the use of fluorescent dyes at high concentrations results in difficulty in emitting light of high luminance by concentration quenching or association.
On the other hand, organic light emitting devices realizing luminescence of high luminance are elements in which organic materials are applied by vacuum deposition. The fabrication of the elements by coating is preferred from the viewpoints of simplification of manufacturing processes, processability and enlargement of area. However, the elements fabricated by the conventional coating system are inferior in luminance and light emitting efficiency to the element fabricated by vapor deposition. It has been therefore a great problem to make it possible to emit light of high luminance at high efficiency.
It is therefore a primary object of the present invention to provide materials for light emitting devices good in light emitting characteristics and excellent in stability in repeated use thereof, and the light emitting devices. A secondary object of the present invention is to provide light emitting devices excellent in color purity, and materials for the light emitting devices making it possible. A third object of the present invention is to provide novel heterocyclic compounds effective in various electronic devices.
These objects have been attained by the following means:
(1) A material for a light emitting device consisting of a compound represented by the following general formula (I):
L"Parenopenst"A)mxe2x80x83xe2x80x83(I)
wherein A represents a heterocyclic group in which two or more aromatic heterocycles are condensed; m represents an integer of 2 or more, and the heterocyclic groups represented by A may be the same or different; and L represents a connecting group;
(2) A material for a light emitting device consisting of a compound represented by the following general formula (II):
L"Parenopenst"B)mxe2x80x83xe2x80x83(II)
wherein B represents a heterocyclic group in which two or more 5- and/or 6-membered aromatic heterocycles are condensed; m represents an integer of 2 or more, and the heterocyclic groups represented by B may be the same or different; and L represents a connecting group;
(3) A material for a light emitting device consisting of a compound represented by the following general formula (III): 
wherein X represents O, S, Se, Te or Nxe2x80x94R; R represents a hydrogen atom, an aliphatic hydrocarbon group, an aryl group or a heterocyclic group; Q3 represents an atomic group necessary to form an aromatic heterocycle; m represents an integer of 2 or more; and L represents a connecting group;
(4) A material for a light emitting device consisting of a compound represented by the following general formula (IV): 
wherein X represents O, S, Se, Te or Nxe2x80x94R; R represents a hydrogen atom, an aliphatic hydrocarbon group, an aryl group or a heterocyclic group; Q4 represents an atomic group necessary to form a nitrogen-containing aromatic heterocycle; m represents an integer of 2 or more; and L represents a connecting group;
(5) A material for a light emitting device consisting of a compound represented by the following general formula (V): 
wherein X5 represents O, S or Nxe2x80x94R; R represents a hydrogen atom, an aliphatic hydrocarbon group, an aryl group or a heterocyclic group; Q5 represents an atomic group necessary to form a 6-membered nitrogen-containing aromatic heterocycle; m represents an integer of 2 or more; and L represents a connecting group;
(6) A material for a light emitting device consisting of a compound represented by the following general formula (VI): 
wherein X6 represents O, S or Nxe2x80x94R; R represents a hydrogen atom, an aliphatic hydrocarbon group, an aryl group or a heterocyclic group; Q6 represents an atomic group necessary to form a 6-membered nitrogen-containing aromatic heterocycle; n represents an integer of 2 to 8; and L represents a connecting group;
(7) A material for a light emitting device consisting of a compound represented by the following general formula (VII): 
wherein R represents a hydrogen atom, an aliphatic hydrocarbon group, an aryl group or a heterocyclic group; Q7 represents an atomic group necessary to form a 6-membered nitrogen-containing aromatic heterocycle; n represents an integer of 2 to 8; and L represents a connecting group;
(8) A material for a light emitting device consisting of a compound represented by the following general formula (VIII): 
wherein Q81, Q82 and Q83 each represents an atomic group necessary to form a 6-membered nitrogen-containing aromatic heterocycle; R91, R92 and R93 each represents a hydrogen atom, an aliphatic hydrocarbon group, an aryl group or a heterocyclic group; L1, L2 and L3 each represents a connecting group; and Y represents a nitrogen atom or a 1,3,5-benzenetriyl group;
(9) A compound represented by the following general formula (IX): 
wherein Q91, Q92 and Q93 each represents an atomic group necessary to form a 6-membered nitrogen-containing aromatic heterocycle; and R91, R92 and R93 each represents a hydrogen atom, an aliphatic hydrocarbon group, an aryl group or a heterocyclic group;
(10) A compound represented by the following general formula (X): 
wherein R101, R102 and R103 each represents a hydrogen atom, an aliphatic hydrocarbon group, an aryl group or a heterocyclic group; R104, R105 and R106 each represents a substituent; and p1, p2 and p3 each represents an integer of 0 to 3;
(11) A material for a light emitting device consisting of a compound represented by the following general formula (XI): 
wherein Q3 represents an atomic group necessary to form an aromatic heterocycle; R11 represents a hydrogen atom or a substituent; m represents an integer of 2 or more; and L represents a connecting group;
(12) A light emitting device comprising a light emitting layer or a plurality of organic compound films containing a light emitting layer formed between a pair of electrodes, wherein at least one layer is a layer containing at least one of the compounds represented by general formula (I) to (XI) described in (1) to (11);
(13) A light emitting device comprising a light emitting layer or a plurality of organic compound films containing a light emitting layer formed between a pair of electrodes, wherein at least one layer is a layer in which at least one of the compounds represented by general formula (I) to (XI) described in (1) to (11) is dispersed in a polymer;
(14) A light emitting device comprising a light emitting layer or a plurality of organic compound films containing a light emitting layer formed between a pair of electrodes, wherein at least one layer between the light emitting layer and a cathode is a layer containing at least one of the compounds represented by general formula (I) to (XI) described in (1) to (11);
(15) A light emitting device comprising a light emitting layer or a plurality of organic compound films containing a light emitting layer formed between a pair of electrodes, wherein at least one layer between a blue light emitting layer and a cathode is a layer containing at least one of the compounds represented by general formula (I) to (XI) described in (1) to (11); and
(16) A light emitting device comprising a light emitting layer or a plurality of organic compound films containing a light emitting layer formed between a pair of electrodes, wherein a layer containing at least one of the compounds represented by general formula (I) to (XI) described in (1) to (11) contains a blue light emitting material.